I always ship within 1 working day.
When I do custom orders, I don't use Etsy's system. I just have the customer contact me, I make their order, get their approval, list the product, the customer buys it and, again, I ship it within 1 working day.
But I understand that not every seller on Etsy can ship that fast, even if they wanted to.
I don't have a day job besides my creative business and my post office is only a five minutes walk from my home (I take a daily walk in the morning anyway, for health reasons). So it is easy for me to reach this goal. Not every seller has this luxury.
I am located in Europe though, while most of my customers are in the US, so it is basically up to the USPS to deliver my packages in time.
It usually takes 5-12 days, because most of my products can be shipped by letter mail and don't get hold up in customs.